Extraction-spectrophotometric determination of vanadium with 5,5′-dithiodisalicylhydroxamic acid (DTDSHA)

A new method for the extraction-spectrophotometric determination of V(V) is proposed. The violet complex V(V)-5,5′-dithiodisalicylhydroxamic acid formed in aqueous medium (pH 5.0) is extracted into a solution of trioctylmethylammonium chloride (Adogen 464) in toluene, and its spectrophotometric characteristics are studied. The stoichiometry of the complexes formed is 1:1 and 2:1 (reagent:vanadium), and 1:3 for the ionic association complex (2:1):trioctylmethylammonium ion. The system follows Beer's law at pH 5.0 (λ = 550 nm) over the concentration range 0.4 to 2.0 ppm (ε = 7.34 × 10³ liter · mol⁻¹ · cm⁻¹). The method is applied for the determination of vanadium in steel.     

Vanadium(V) environments in bismuth vanadates: A structural investigation using Raman spectroscopy and solid state V NMR

The Bi₂O₃---V₂O₅ system was examined using Raman spectroscopy and solid state ⁵¹V wideline, magic-angle spinning (MAS), and nutation NMR spectroscopy. The methods are shown to be complementary in the identification of the various phases and in the characterization of their vanadium site symmetries. Most of the compositions examined (1:1 ≤ Bi:V ≤ 60:1) are multiphasic. Depending on the Bi:V ratio, the following phases have been identified: BiVO₄, Bi₄V₂O₁₁, a triclinic type-II phase, a cubic type-I phase, γ-Bi₂O₃ doped with V(V) (sillenite), and β-Bi₂O₃. Detailed spectroscopic characterization reveals that vanadium is tetrahedrally coordinated in all these compounds, and that the degree of symmetry increases with increasing Bi:V ratio. At the highest Bi:V ratios, the combined interpretation of the Raman and NMR data provides strong evidence for the presence of Bi⁵⁺O₄ tetrahedra.     

51V solid-state magic angle spinning NMR spectroscopy and DFT studies of oxovanadium(V) complexes mimicking the active site of vanadium haloperoxidases

A series of 11 oxovanadium(V) complexes mimicking the active site of vanadium haloperoxidases have been investigated by (51)V magic angle spinning NMR spectroscopy and density functional theory (DFT). The MAS spectra are dominated by the anisotropic quadrupolar and chemical shielding interactions; for these compounds, C(Q) ranges from 3 to 8 MHz, and delta(sigma) is in the range 340-730 ppm. The quadrupolar coupling and chemical shielding tensors as well as their relative orientations have been determined by numerical simulations of the spectra. The spectroscopic NMR observables appear to be very sensitive to the details of the electronic and geometric environment of the vanadium center in these complexes. For the four crystallographically characterized compounds from the series, the quadrupolar and chemical shielding anisotropies were computed at the DFT level using two different basis sets, and the calculated tensors were in general agreement with the experimental solid-state NMR data. A combination of (51)V solid-state NMR and computational methods is thus beneficial for investigation of the electrostatic and geometric environment in diamagnetic vanadium systems with moderate quadrupolar anisotropies.     

Complex of vanadium(5+) with the dioxygen radical-anion in the catalyzed disproportionation of hydrogen peroxide

Conclusions The intermediate formation of vanadium(5+) peroxo complexes was detected under conditions of the disproportionation of hydrogen peroxide in acetic acid catalyzed by ammonium metavanadate by⁵¹V NMR spectroscopy and the complex of vanadium(5+) ions with the dioxygen radical-anion was detected by ESR spectroscopy.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1914–1917, August, 1985.     

Multinuclear magnetic resonance study of some imidovanadium complexes

¹⁴N NMR studies were carried out for a series of mononuclear and dinuclear vanadium complexes with different types of nitrogen ligands (terminal and µ‐imido, amido, nitrido, amine). Some complexes containing ancillary phosphine moieties were also characterized by ³¹P NMR spectroscopy. The observed shieldings for terminal and bridging imido ligands are intermediate between those of nitrido and amido moieties, and the latter appear less shielded than coordinated tertiary amines. The ranges for individual ligand types are sufficiently resolved to allow the use of nitrogen chemical shifts as a structure assignment tool. The ¹⁴N NMR signals of terminal and bridging imido nitrogens displayed marked differences in their lineshapes which could be used as an additional criterion for signal assignment. Examination of substituent influences revealed the absence of a general parallelism between δ¹⁴N and δ⁵¹V, but gave evidence for parallel relationships between both quantities for complexes with formal 12VE and 16VE electron counts. Determination of ¹J(⁵¹V,¹⁴N) and ¹J(⁵¹V,³¹P) coupling constants in mononuclear complexes was feasible from simulation of ¹⁴N and ³¹P lineshapes and suggested that imido ligands exhibit generally greater couplings to vanadium than amido ligands. Analysis of the ³¹P {¹H,¹⁴N} NMR spectrum allowed us to determine ²J(⁵¹V,³¹P) for the vanadacycle cyclo(^tBuN—P?C(^tBu)—VCl₃—). It was shown that both couplings can be employed for the acquisition of two‐dimensional ³¹P,⁵¹V shift correlations. Copyright © 2001 John Wiley & Sons, Ltd.     

The Effect of Growth Parameters on Electrophysical and Memristive Properties of Vanadium Oxide Thin Films

We have experimentally studied the influence of pulsed laser deposition parameters on the morphological and electrophysical parameters of vanadium oxide films. It is shown that an increase in the number of laser pulses from 10,000 to 60,000 and an oxygen pressure from 3 × 10⁻⁴ Torr to 3 × 10⁻² Torr makes it possible to form vanadium oxide films with a thickness from 22.3 ± 4.4 nm to 131.7 ± 14.4 nm, a surface roughness from 7.8 ± 1.1 nm to 37.1 ± 11.2 nm, electron concentration from (0.32 ± 0.07) × 10¹⁷ cm⁻³ to (42.64 ± 4.46) × 10¹⁷ cm⁻³, electron mobility from 0.25 ± 0.03 cm²/(V·s) to 7.12 ± 1.32 cm²/(V·s), and resistivity from 6.32 ± 2.21 Ω·cm to 723.74 ± 89.21 Ω·cm. The regimes at which vanadium oxide films with a thickness of 22.3 ± 4.4 nm, a roughness of 7.8 ± 1.1 nm, and a resistivity of 6.32 ± 2.21 Ω·cm are obtained for their potential use in the fabrication of ReRAM neuromorphic systems. It is shown that a 22.3 ± 4.4 nm thick vanadium oxide film has the bipolar effect of resistive switching. The resistance in the high state was (89.42 ± 32.37) × 10⁶ Ω, the resistance in the low state was equal to (6.34 ± 2.34) × 10³ Ω, and the ratio R_HRS/R_LRS was about 14,104. The results can be used in the manufacture of a new generation of micro- and nanoelectronics elements to create ReRAM of neuromorphic systems based on vanadium oxide thin films.     

The Chemistry of Vanadium bis-Phenolate NHC Complexes in Three Oxidation States

Twenty-one vanadium bis-phenolate benzimidazolylidene complexes, spanning three oxidation states, have been investigated. Special emphasis is placed on their salt metathesis reactivity and the accessibility of the +IV oxidation state by reductive or oxidative routes, starting from vanadium(V) or vanadium(III) respectively. While the reductive route is highly dependent on the reducing agent and starting material used, the oxidative route gives clean access to vanadium(IV) dihalide complexes. The low-valent vanadium(III) complexes are excellent precursors for salt metathesis reactions which lead to the isolation of a rare vanadium(III) NHC alkyl complex. All new complexes have been characterized by (paramagnetic) ¹H NMR and ⁵¹V NMR, UV–VIS, IR and EPR spectroscopy as well as elemental analysis. Cyclic voltammetry has been performed in selected cases to study the influence of imido or phenolate supporting ligands towards the redox-potential of the vanadium(V/IV) redox couple compared to the parent oxo-chlorido complex A .     

Investigating the vanadium environments in hydroxylamido V(V) dipicolinate complexes using 51V NMR spectroscopy and density functional theory

Using (51)V magic angle spinning solid-state NMR, SSNMR, spectroscopy and quantum chemical DFT calculations we have characterized the chemical shift and quadrupolar coupling parameters of a series of eight hydroxylamido vanadium(V) dipicolinate complexes of the general formula VO(dipic)(ONR1R2)(H2O) where R1 and R2 can be H, CH3, or CH2CH3. This class of vanadium compounds was chosen for investigation because of their seven-coordinate vanadium atom, a geometry for which there is limited (51)V SSNMR data. Furthermore, a systematic series of compounds with different electronic properties are available and allows for the effects of ligand substitution on the NMR parameters to be studied. The quadrupolar coupling constants, C(Q), are small, 3.0-3.9 MHz, but exhibit variations as a function of the ligand substitution. The chemical shift tensors in the solid state are sensitive to changes in both the hydroxylamide substituent and the dipic ligand, a sensitivity which is not observed for isotropic chemical shifts in solution. The chemical shift tensors span approximately 1000 ppm and are nearly axially symmetric. On the basis of DFT calculations of the chemical shift tensors, one of the largest contributors to the magnetic shielding anisotropy is an occupied molecular orbital with significant vanadium d(z)2 character along the V=O bond.     

Characterization of noninnocent metal complexes using solid-state NMR spectroscopy: o-dioxolene vanadium complexes

(51)V solid-state NMR (SSNMR) studies of a series of noninnocent vanadium(V) catechol complexes have been conducted to evaluate the possibility that (51)V NMR observables, quadrupolar and chemical shift anisotropies, and electronic structures of such compounds can be used to characterize these compounds. The vanadium(V) catechol complexes described in these studies have relatively small quadrupolar coupling constants, which cover a surprisingly small range from 3.4 to 4.2 MHz. On the other hand, isotropic (51)V NMR chemical shifts cover a wide range from -200 to 400 ppm in solution and from -219 to 530 ppm in the solid state. A linear correlation of (51)V NMR isotropic solution and solid-state chemical shifts of complexes containing noninnocent ligands is observed. These experimental results provide the information needed for the application of (51)V SSNMR spectroscopy in characterizing the electronic properties of a wide variety of vanadium-containing systems and, in particular, those containing noninnocent ligands and that have chemical shifts outside the populated range of -300 to -700 ppm. The studies presented in this report demonstrate that the small quadrupolar couplings covering a narrow range of values reflect the symmetric electronic charge distribution, which is also similar across these complexes. These quadrupolar interaction parameters alone are not sufficient to capture the rich electronic structure of these complexes. In contrast, the chemical shift anisotropy tensor elements accessible from (51)V SSNMR experiments are a highly sensitive probe of subtle differences in electronic distribution and orbital occupancy in these compounds. Quantum chemical (density functional theory) calculations of NMR parameters for [VO(hshed)(Cat)] yield a (51)V chemical shift anisotropy tensor in reasonable agreement with the experimental results, but surprisingly the calculated quadrupolar coupling constant is significantly greater than the experimental value. The studies demonstrate that substitution of the catechol ligand with electron-donating groups results in an increase in the HOMO-LUMO gap and can be directly followed by an upfield shift for the vanadium catechol complex. In contrast, substitution of the catechol ligand with electron-withdrawing groups results in a decrease in the HOMO-LUMO gap and can directly be followed by a downfield shift for the complex. The vanadium catechol complexes were used in this work because (51)V is a half-integer quadrupolar nucleus whose NMR observables are highly sensitive to the local environment. However, the results are general and could be extended to other redox-active complexes that exhibit coordination chemistry similar to that of the vanadium catechol complexes.     

Group 9 half-sandwich complexes containing the unique P,P′-diphenyl-1,4-diphospha-cyclohexane ligand: Synthesis, X-ray structure analyses and spectroscopic studies

We wish to report the synthesis and characterization of Group 9 metal complexes with the novel P,P′-diphenyl-1,4-diphospha-cyclohexane (dpdpc) ligand. The complexes are readily prepared by direct ligand substitution reactions from the dichloro-bridged binuclear complexes, [{η⁵-Cp*M(Cl)₂}₂]. The complexes include: [η⁵-Cp*Rh(Cl)₂]₂(μ-dpdpc) (1), [η⁵-Cp*Ir(Cl)₂]₂(μ-dpdpc) (2), and [η⁵-Cp*Rh(Cl)(dpdpc)]PF₆ (3). The structures for all three complexes are supported by ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy as well as elemental analysis. The molecular structures of 1 and 3 have also been established by single-crystal X-ray analysis.     

NMR Crystallography of an Oxovanadium(V) Complex by an Approach Combining Multinuclear Magic Angle Spinning NMR,DFT, and Spin Dynamics Simulations

Bioinorganic vanadium(V) solids are often challenging for structural analysis. Here, we explore an NMR crystallography approach involving multinuclear ¹³C/⁵¹V solid‐state NMR spectroscopy, density functional theory (DFT), and spin dynamics numerical simulations, for the spectral assignment and the 3D structural analysis of an isotopically unmodified oxovanadium(V) complex, containing 17 crystallographically inequivalent ¹³C sites. In particular, we report the first NMR determination of C–V distances. So far, the NMR observation of ¹³C–⁵¹V proximities has been precluded by the specification of commercial NMR probes, which cannot be tuned simultaneously to the close Larmor frequencies of these isotopes (100.6 and 105.2 MHz for ¹³C and ⁵¹V, respectively, at 9.4 T). By combining DFT calculations and ¹³C–⁵¹V NMR experiments, we propose a complete assignment of the ¹³C spectrum of this oxovanadium(V) complex. Furthermore, we show how ¹³C–⁵¹V distances can be quantitatively estimated.     

Ethylisobutrazine hydrochloride as a selective and sensitive reagent for the spectrophotometric determination of vanadium(V) and its application to vanadium-bearing minerals and alloys

Ethylisobutrazine hydrochloride is proposed as a selective and sensitive reagent for the spectrophotometric determination of vanadium(V). It forms a red-colored species with vanadium(V) in 3.5–6.5 M phosphoric acid medium. An eight-fold molar excess of reagent is necessary for the full development of the color. The red species exhibits an absorption maximum at 518 nm with a molar absorptivity of 9.75 × 10³ liters mol⁻¹ cm⁻¹. Sandell's sensitivity is 5.2 ng cm⁻². Beer's law is obeyed over the range 0.1–6.2 ppm of vanadium(V) with an optimum concentration range of 0.4–6.0 ppm. The effects of acidity, time, temperature, order of addition of reagents, reagent concentration, and the interferences from various ions, are reported. The method has been used successfully for the determination of vanadium in ilmenite and vanadium steels that contain chromium, molybdenum, manganese, nickel, copper, tungsten, and titanium.     

51V and 17O NMR studies of the mixed metal polyanions in aqueous V—Mo solutions

NaVO₃Na₂MoO₄ solutions acidified with HCl were studied at the atomic V/Mo ratios equal to 3 : 1, 1 : 1, 1 : 3, 1 : 6 and vanadium concentration [V] = 0.1, 0.04, 0.004 and 0.0004 M in the range pH 7-2. Their ⁵¹V NMR spectra (measured at H_ito = 7 T) were compared with those of VW solutions containing mixed metal complexes of known composition. The VMo₅O₁₉³⁻ (⁵¹V NMR chemical shift relative to VOCl₃, δ, −502 ppm), V₂Mo₄O₁₉⁴⁻ (δ −494), V₂Mo₄O₁₉³⁻ δ −507), V₉MoO₂₈⁵⁻ (δ −422, −492, −501, −512, −521.5) and HV₉MoO₂₈⁴⁻ polyanions (p.a.) have been found to be dominant mixed species in Na-V-Mo solutions. Along with them the V_itxMO_13-itxO^−itx−3₄₀ p.a.(x∼2–3) of the Keggin type (δ −496, −498, −516, −522) are supposed to be formed at pH < 4 in concentrated solutions ([V] > 0.01 M). The V₂Mo₆O₂₆⁶⁻ p.a., isolated at pH ∼ 5 as the sodium salt (solid state δ −482), seem to be present in concentrated Na-V-Mo solutions only as minor species. On dissolving the salt the V₂Mo₆O₂₆⁶⁻ p.a. mainly disproportionates into the complexes mentioned. From solutions containing mainly the V₉MoO₂₈⁵⁻ p.a. the sodium salt of V₁₀O₂₈⁶⁻ is crystallized. The V₉WO₂₈⁶⁻ p.a. are detected in VW solutions at V/W > 1. ¹⁷O and ⁹⁵Mo NMR spectra of some mixed complexes are described. The distribution diagrams for VMo and V-W solutions at [V] = 0.004 M and V/Mo(W) = 1:3, derived from their ⁵¹V NMR spectra, are given.     

Selective Sorption–Spectrometric Determination of Nanogram Amounts of Vanadium(IV) and Vanadium(V)

Conditions of the selective sorption–spectrometric determination of vanadium(IV) and vanadium(V) using sulfonitrophenol M were found. The determination of vanadium (visual test (RSD = 30%) using a reference color scale or quantitative determination (RSD < 10%) by diffuse reflectance spectra is performed immediately after the dynamic-mode sorption of its colored complexes with sulfonitrophenol M at pH 3.5 (vanadium(IV)) or with sulfonitrophenol M and hydroxylamine at pH 1.5 (vanadium(V), 650 nm) at the surface of polyamide membrane disks (d= 1 cm, l= 0.1 mm, m= 2.7 mg). The flow rate is 10–20 mL/min. The detection limit is 5–7 ng of vanadium in the support zone or 0.2–0.5 ng/mL. The determination of 0.5–5 ng/mL vanadium(V) at pH 1.5 does not interfere with 20-fold amounts of V(IV) and 1000-fold amounts of Ni, Zn, Cd, Mg, Co, Cr(III), Mn, PO^3- ₄, and F^–.     

The coordinative properties of the ligands Ph2ECH2EPh2 (E = P,As, Sb) in carbonylvanadium complexes,and the molecular structure of η5-C5H5V(CO)3As2Ph4

Photo-reaction between the ligands Ph₂ECH₂EPh₂ (E = P: dppm, E = As: dpam, E = Sb: dpsm), L, and the vanadium complexes η⁵-C₅H₅V(CO)₄ and [Et₄N][V(CO)₆] yields monosubstituted mononuclear (dpsm) and dinuclear, ligand-bridged complexes (dpam, dpsm). With dppm, the final products are disubstituted chelate complexes, but monosubstituted mono- and dinuclear species are formed as intermediates.The shielding of the ⁵¹V nucleus decreases in the series dpsm > dppm > dpam and {M(CO)_n} > {M(CO)_n?1} L > {M(CO)_n?1}₂μ-L > {M(CO)_n?2}dppm ({M(CO)_n}[V(CO)₆]^?, η⁵-C₅H₅V(CO)₄). The half-widths of the NMR signals are greater for dinuclear than for mononuclear complexes.The crystal and molecular structures of η⁵-C₅H₅V(CO)₃As₂Ph₄ have been determined. The compound crystallizes in the space group P2₁/c with a = 1347.8, b = 1020.0, c = 2085.2 pm and β = 82.3°. Due to steric crowding, the ⁵¹V shielding is low composed to that of {η⁵-C₅H₅V(CO)₃}₂μ-dpam.     

Catalysis of hydrosilylation by well-defined rhodium siloxide complexes immobilized on silica

Rhodium surface siloxide complexes were prepared directly by condensation of the molecular precursors ([{Rh(μ-OSiMe₃)(cod)}₂], [{Rh(μ-OSiMe₃)(tfb)}₂], [{Rh(μ-OSiMe₃)(nbd)}₂]) with silanol groups on silica surface (Aerosil 200 and SBA-15) and their structures were characterized by ¹³C and ²⁹Si CP/MAS NMR spectroscopy. Such single-site complexes were tested for their activity in hydrosilylation of carbon–carbon double bonds with triethoxysilane, heptamethyltrisiloxane and poly(hydro,methyl)(dimethyl)siloxane. The best catalyst appeared to be cyclooctadiene ligand-containing rhodium siloxide complex immobilized on Aerosil which was recycled as many as 20 times without loss of activity and selectivity in hydrosilylation of vinylheptamethyltrisiloxane with heptamethyltrisiloxane. On the ground of CP/MAS NMR measurements it was established that the mechanism of hydrosilylation catalyzed by silica-supported rhodium siloxide complexes is different from that for the complexes in the homogeneous system.     

Determination of traces of vanadium with the catalytic maximum wave in differential pulse polarography

Summary A differential pulse-polarographic method has been studied for the determination of vanadium employing the catalytic maximum wave. A well-defined differential pulse polarographic peak is observed in the potential range from –0.2 to –0.7 V vs. SCE for vanadium(V) in 10 mmol 1^–1 NaCl containing 10 mmol 1^–1 acetic acid, 40 mmol 1^–1 pyrocatechol, and 2.5 mmol 1^–1 KBrO₃. The peak current is very large and proportional to the concentration of vanadium(V) between 1×10^–7 and 1×10^–6 mol 1^–1. The relative standard deviation at 0.5 mol l^–1 vanadium(V) was 2.06% (n=7). This method has been successfully applied to the determination of vanadium in standard materials such as pond sediment.

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Spurenbestimmung von Vanadium mit Hilfe der katalytischen Maximumsstufe in der Differential-Puls-Polarographie

Zusammenfassung Ein gut definierter differentialpuls-polarographischer Peak wurde für Vanadium(V) in 10 mmol/l NaCl-Lösung, die 10 mmol/l Essigsäure, 40 mmol/l Brenzcatechin und 2,5 mmol/l KBrO₃ enthielt, beobachtet (Potentialbereich –0,2 bis –0,7 V gegen SCE). Der Peakstrom ist sehr groß und die Vanadiumkonzentration im Bereich von 1×10^–7 bis 1×10^–6 mol/l proportional. Die relative Standardabweichung betrug 2,06% (n=7) bei 0,5 mol/l Vanadium(V). Das Verfahren wurde mit gutem Erfolg zur Vanadiumbestimmung in Standardproben (z.B. Teichsediment) eingesetzt.

     

Vanadium(V) extraction from sulfuric acid solutions

We studied vanadium(V) extraction by di-2-ethylhexylphosphoric acid (DEHPA) from 1.0–12.0 M sulfuric acid. Optimal extraction parameters were determined. IR, ⁵¹V NMR, and electronic spectroscopy was used to determine the stoichiometry of the extracted complex and the reaction equation for vanadium(V) extraction by DEHPA. The equilibrium constant of vanadium(V) extraction by DEHPA was determined.     

Synthesis and catalytic properties of novel ruthenium N-heterocyclic-carbene complexes

The reaction of [RuCl₂(p-cymene)]₂ with 1,3-dialkylimidazolinium salts 1a–f in the presence of a small excess of cesium carbonate yields chelated η⁶-arene, η¹-carbene ruthenium complexes 2a–f. All synthesised compounds were characterized by elemental analysis, NMR spectroscopy. The catalytic activity of RuCl₂(η⁶-arene, η¹-imidazolinylidene) complexes 2a–f was evaluated in the direct arylation of 2-phenylpyridine with chlorobenzene derivatives.     

Intramolecular rearrangements of cyclooctadienerhodium(I) fragments supported on a vanadium oxide cluster as evidenced by dynamic17O NMR spectroscopy

Variable-temperature¹⁷O NMR together with⁵¹V and¹⁰³Rh NMR studies on newly prepared vanadium oxide-supported organorhodium(I) fragment(s), [(RhCOD) _n (V₄O₁₂)]^(4–n)– (n = 1, 2; COD = ⁴-1,5-cyclooctadiene) indicate that intramolecular rearrangements of RhCOD fragment(s) on a vanadium oxide surface occur in solution.